Question

已知X分之1-Y分之1=5,求X-3XY-Y分之3X+5XY-3Y的值

Answer 1

1/x－1/y＝5,通分得：

(y-x)/(xy)＝5,即

y－x＝5xy,或写作

x－y＝-5xy,代入所求式,得：

(3x+5xy-3y)/(x-3xy-y)

＝[3(x-y)+5xy]/[(x-y)-3xy]

＝(-15xy+5xy)/(-5xy-3xy)

＝(-10xy)/(-8xy)

＝5/4